This invention relates to a welding device for carrying out a continuous welding operation, and more particularly relates to a welding device for use with an elongated welding electrode having a welding flux coating provided thereon. The flux coating has a plurality of gaps formed at even intervals along its entire length to expose the metal core within the electrode.
A continuous welding operation may be carried out with an elongated welding electrode having a welding flux coating provided thereon. As shown in Applicant's copending continuation-in-part application No. 08/427,408, filed on Apr. 24, 1995, now pending, a plurality of slots or gaps may be provided at equal intervals in the flux coating such that the welding current may be applied to the metal core of the electrode through these gaps to provide a high current required for the welding operation. In order to carry out the welding operation, the welding electrode may be driven through a welding device by a plurality of contact carriers mounted on one or two drive chains. The contact carriers not only apply the high welding current to the plurality of contact points in the metal core defined by the gaps in the flux coating but also engage these gaps for advancing the electrode continuously towards the welding area. Such a welding device is shown in Applicant's copending application No. 08/343,021, filed on Sep. 12, 1994, now U.S. Pat. No. 5,448,217. Although such chain driven welding device is efficient in providing the welding operation, it has several drawbacks. Firstly, in order for the contact element to move freely by the drive chain movably mounted on a rotary wheel located at the front end of the housing of the welding device, a relatively large area in the housing must be provided to accommodate at least the radius of the rotary drive wheel plus the width of the drive chain plus the width of the contact element. The total width of these elements invariably increases the effective distance between the front end of the welding electrode to the current contact point closest to this front end. Thus, the current must pass through a relatively long length of electrode between these two points to the welding area, and it reduces the efficiency of the welding current due to the resistance loss passing through such relatively long length of the electrode. Typically, for a chain driven welding device using a common welding electrode of 2.0 mm in diameter and having a plurality of contact slots formed 38.1 mm apart from one another in the flux coating, the minimum distance between the welding area to the closest current contact point is at least 10 cm long, and the effective welding current obtained at the welding area is often less than 200 A which is not sufficient for producing a high quality weld. Furthermore, the welding device, particularly for a double drive chain device, must have an even larger size then the above in order to house the drive chains, their rotary drive wheels and the driving mechanism as well as to provide the space for the contact elements to be circulated within its housing. For this reason, the chain driven welding devices are rather bulky in size and heavy in weight and they are not conducive for handheld application due to the difficulty in having to manoeuvre such large size and heavy weight.
Another drawback of the chain driven welding devices is that the drive chains, after even a short period of use, tend to become slacken due to wear. The slack in turn causes the contact elements mounted thereon to become misaligned with the welding electrode such that the latter may become jammed in the device, or the flux coating on the electrode is torn by the misaligned contact elements. Also, a poor contact engagement may result between the contact fingers of the contact elements and the metal core of the welding electrode. The poor contact not only reduces the effective amount of welding current provided to the welding area and seriously affecting the quality of the weld and it also inherently generates harmful heat at the contact points. Such undesirable heat accelerates the deterioration of the contacts and it may also raise the body temperature of the welding device housing to an unmanageable degree for handheld operation.